(a) Field of the Invention
This invention relates to arterial blood pressure monitoring and more particularly to a method and apparatus for continuous and nonn-contactive blood pressure measurement.
(b) Description of the Prior Art
Continuous blood pressure monitoring techniques suffer from the problems of either being invasive or occluding the flow of blood. Invasive measurement, by way of arterial catheterization has been commonly used in intensive care units and operating rooms for a number of years. However, the risks of infection, thrombus formation, hemorrhage, etc., have given rise to a search for non-invasive approaches which would provide the desired continuous and accurate measurement.
The typical non-invasive approaches taken to date include devices using the so-called tracking cuff principle, e.g., see U.S. Pat. No. 4,524,777. The device disclosed in this patent utilizes a hydraulic servocontrol system to maintain a finger arterial volume constant (in an unloaded state) so that the counter cuff pressure follows the intraarterial blood pressure thus giving an instantaneous arterial blood pressure measurement from the counter cuff pressure. Although this method does provide continuous and non-invasive measurement of arterial blood pressure, long-term maintenance of cuff pressure restrains microcirculation in the finger capillaries and this causes pain. Also, a downward drift occurs for some period of time before stability is reached.
One other non-invasive approach, but which is not continuous, uses a sphygmomanometric technique based on Riva-Rocci's principle in which auscultatory (sound) measurements of blood flow are made to determine the arterial blood pressure (systolic and diastolic only), again using cuff pressure. These measurements are less desirable not only because they are not continuous but also because they are not as accurate.
Another non-invasive approach, known as the oscillometric method, utilizes volume measurements, rather than auscultatory measurements, and cuff pressure to more accurately determine systolic blood pressure. This method also measures mean blood pressure, but not diastolic pressure.
An accurate, non-invasive, continuous and non-occlusive (does not occlude the flow of blood) apparatus and method would be valuable for use in intensive care units and operating rooms to avoid complications which can arise with the above-described prior art devices and methods.